1. Field of the Invention
This invention relates to the selection and treatment of seeds, including in particular, but not limited to, hybrid corn seeds.
2. Introduction to the Invention
Yields from seeds depend on the rate and uniformity at which the seeds germinate (as well as other factors such as seed quality, soil quality, the presence of fungi and/or insects, and weather conditions). The rate and uniformity of germination depend on the temperature and moisture content of the soil after the seeds have been planted (as well as other factors). For example, for corn seeds, a soil temperature of 15° C. or higher and a soil moisture content of about 21% are generally regarded as ideal. If the soil temperature and moisture content are too low, germination is poor and nonuniform. If the soil moisture content is satisfactory, but the soil temperature too low, the seeds suffer chilling injury, because they imbibe water which, at the low temperature, causes cell damage. When the soil warms up, germination is poor and nonuniform. In efforts to insure satisfactory germination, farmers generally try to gauge the optimum time for planting, and plant all their seed over a limited time.
It is known to treat seeds with liquid or solid compositions containing active agents which will, directly or indirectly, increase the yield from the seeds. The active agent(s) can for example be applied to the seeds in a liquid composition containing a water-soluble or water-dispersible polymeric binder which, after the composition has solidified, binds the active agent(s) to the seeds. For example, it is common practice, in order to reduce damage by fungi, to treat seeds with compositions containing one or more fungicides. The term “fungicide-treated seeds” is used herein to denote seeds which (i) have a coating thereon comprising a fungicide and binder, the coating being discontinuous and/or the binder being water-soluble or water-dispersible, and (ii) do not have a continuous polymeric coating thereon. It has also been proposed to coat seeds with temperature-sensitive polymers, for example side chain crystalline (SCC) polymers. For further information about known methods of coating seeds, reference to may be made for example to U.S. Pat. No. 3,598,565 (Graves), U.S. Pat. No. 3,698,133 (Schreiber), U.S. Pat. No. 3,808,740 (Porter et al), U.S. Pat. No. 4,238,523 (Porter et al), U.S. Pat. No. 4,251,952 (Porter et al), U.S. Pat. No. 4,272,417 (Barke et al.), U.S. Pat. No. 4,344,979 (Gago), U.S. Pat. No. 4,735,017 (Gago et al), U.S. Pat. No. 4,879,839 (Gago et al), U.S. Pat. No. 5,129,180 (Stewart), U.S. Pat. No. 5,843,982 (Leadbitter), U.S. Pat. No. 5,849,320 (Turnblad et al), U.S. Pat. No. 5,876,739 (Turnblad et al), U.S. Pat. No. 6,199,318 B1 (Stewart et al) and U.S. Pat. No. 6,329,319 B1 (Puglisi et al), the entire disclosures of which are incorporated herein by reference for all purposes.
In order to supply reliable seeds, suppliers of fungicide-treated seeds often subject samples from each seed lot to one or more tests in which the germination percentage is measured under controlled conditions. The seed lots that pass the test(s) are then sold as high-quality seeds. One such test is a “vigor test” which attempts to forecast germination under a range of field conditions. The vigor tests used by different suppliers differ in details, but typically involve determining germination percentages after 7–14 days at 10° C., followed by 7 days at 25° C.